1. Field of the Invention
The present invention relates to a fuel leakage preventing valve for preventing fuel leakage from a fuel tank at the time, for example, of cornering or rolling-over of an automobile.
2. Description of the Related Art
In a conventional fuel preventing valve, an accommodating chamber is defined inside a housing, and a float valve composed of an outer float and an inner float is arranged in the accommodating chamber so as to be vertically movable. The float valve is upwardly urged by the pressure of a spring, and a valve seat is formed on an upper partition wall side of the accommodating chamber of the housing, with the valve seat being opened and closed by a valve plate held by the float valve. As disclosed, for example, in JP 2003-120449A (corresponding to U.S. Pat. No. 6,508,263), the relationship between the outer float and the inner float of the float valve is as follows: the outer float has on its upper portion a cage portion integrally protruding therefrom, and the inner float is inserted into the outer float from below, with the valve plate being rockably retained in a space defined between the upper portion of the inner float and the cage portion.
In this fuel leakage preventing valve, constructed as described above, the float valve is normally held in the lowered state within the accommodating chamber of the housing, so the valve seat formed in the upper partition wall of the accommodating chamber is open, and fuel vapor within the fuel tank is given off, from a connection tube provided in the housing by way of a canister, to the outside. If some of the fuel in the fuel tank reaches the interior of the accommodating chamber of the housing as a result of cornering, etc. of the automobile, the float valve ascends automatically due to its buoyancy and the pressure of the spring and closes the valve seat with its valve plate, whereby it is possible to prevent fuel leakage toward the canister and further to the outside.
However, in the conventional fuel leakage preventing valve, in which the float valve is composed of the two components of the outer float and the inner float, fuel is likely to gather between the outer float and the inner float, that is, in the space where the valve plate is held. With some fuel accumulated, the float valve itself is subjected to a weight from the fuel so much that it may be impossible for the float valve to close the valve seat with its valve plate unless the liquid level is high. On the other hand, with the fuel drained to leave none or less of it, the float valve itself is subjected to a light weight from the fuel such that the float valve may ascend even if the liquid level is low, thereby closing the valve seat with its valve plate. Thus, these cause a fear of variations in valve closing characteristics.
It might be possible to provide a communication path between the outer float and the inner float in a vertical direction to discharge gathered fuel through this communication path. In this case, however, air would be allowed to flow back in bubbles from this communication path and be guided to the periphery of the valve plate to thereby fluctuate the center of buoyancy of the valve plate. This involves a fear of the sealing property becoming unstable, thus, in any case, conventional fuel leakage preventing valves have merits and demerits.